maintcheck: remove an obsolescent check

maintcheck: remove an obsolescent check

* syntax-checks.mk (sc_test_names): Remove this check, which verified
that no test name contained an m4/m4sugar builtin or macro name.  Since
most tests use their own name as the first argument to AC_INIT, doing
that would have tickled a bug in Autoconf 2.62; but the bug was fixed
in Autoconf 2.63 already; and we are going to soon require Autoconf
2.65 anyway (in automake 1.13), so this check has become more annoying
than useful.
(syntax_check_rules): Don't list the removed check.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>